Heat pipe cooler for differential assembly

ABSTRACT

The present invention is directed to an apparatus to regulate and control the temperature of a differential axle assembly. A heat pipe is inserted though the axle housing with a portion submersed in axle lubricant. Cooling fins are preferably disposed on the heat pipe both in the submersed region of the heat pipe and a portion external the housing. The heat pipe is preferably secured to and substantially accommodated by a removable cover plate which is in turn secured to the housing. The heat pipe includes an evaporative working fluid to promote heat transfer between the lubricant and external environment.

The present application is a Continuation-in-part of U.S. applicationSer. No. 10/143,752 filed on May 14, 2002 and is hereby incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat pipe cooler for a differentialassembly and particularly to an effective evaporative heat pipe assemblyfor transferring heat from the differential lubricant.

2. Description of Related Art

Typically axles are lubricated by a reservoir of oil in the sump whichis circulated by the moving components. This is known as splashlubrication. The operating temperature of a splash lubricated axleassembly or other torque transmission device is generally dependent onthe torque being transmitted, the ambient temperature, the speed ofrotation and airflow over the device.

The operating temperature can be just above the ambient temperature tomore than 200 degrees F. above ambient. Operating temperaturessignificantly above 250 degrees F. can begin to cause problems with thedurability of the components in the axle as well as the lubricantitself. These temperatures are generally encountered at higher speedsand/or torques such as high speed highway driving or trailer towing.Therefore it is desirable to avoid these higher temperatures as much aspossible. It is the intention of the present invention to minimize thesehigh operating temperatures.

It is known to provide cooling conduits within an axle assembly in orderto avoid high operating temperatures. These conduits are positionedabout a majority of the differential assembly and contain a hydraulicfluid from another device which is capable of cooling the lubricant inthe axle.

It is also known to have a differential assembly with a heat pipe havingheat-absorbing portions extending through an oil sump as well asexternally disposed heat-transmitting devices.

Additionally, it is know to have a heat pipe including a closed tubehaving a heat exchange medium comprised of a plurality of fins.

Thus, the aim underlying the present invention lies in providing aneffective fluid lubricant cooling area that is readily utilizable,without significantly increasing the costs of production, the requiredspace, and weight.

SUMMARY OF THE INVENTION

The present invention is directed to a heat pipe cooler for an axlehaving a housing and removable cover. The heat pipe is secured to thecover and includes a heat-receiving zone, a heat-emitting zone and aworking fluid, wherein the working fluid is evaporated in saidheat-receiving zone and condensed in said heat-emitting zone to promoteheat transfer between said lubricant and an external environment. Theheat-receiving zone is at least partially immersed in the lubricant andcontains heat-dissipating fins to promote heat transfer.

BRIEF DESCRIPTIONS OF THE DRAWINGS

A better understanding of the present invention will be had whenreference is made to the accompanying drawings, wherein identical partsare identified by identical reference numbers and wherein:

FIG. 1 is rear view of a differential cover plate with integral heatpipe assembly according to the present invention.

FIG. 2 is a sectional view taken along lines 2-2 of FIG. 1.

FIG. 3 is rear view of a differential cover plate with integral heatpipe assembly according to an alternate embodiment of the presentinvention.

FIG. 4 is a sectional view taken along lines 4-4 of FIG. 3.

FIG. 5 is a sectional view of a heat pipe secured to a differentialcover according to an alternate embodiment of the present invention.

FIG. 6 is a sectional view of a heat pipe secured to a differentialcover according to an alternate embodiment of the present invention.

FIG. 7 is a perspective view of a heat pipe secured to a differentialcover according to an alternate embodiment of the present invention.

FIG. 8 is a front exposed view of the embodiment of FIG. 7.

FIG. 9 is an enlarged partial exposed view of the embodiment of FIG. 8.

FIG. 10 is a sectional view of a heat pipe secured to a differentialcover according to an alternate embodiment of the present invention.

FIG. 11 is a perspective of an installed differential assembly employingthe heat pipe of the present invention.

FIG. 12 is a front view of a heat pipe secured to a differential housingaccording to an embodiment of the present invention.

FIG. 13 is a side view of the embodiment depicted in FIG. 12.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention is directed to a heat pipe assembly for coolinglubricating fluid in a differential axle assembly. Preferably anevaporative heat pipe assembly is employed to increase the amount ofheat transfer from the lubricant to the external environment. Theassembly includes a hermetically sealed heat pipe containing a workingfluid which is secured to a removable cover. The working fluid isselected to be vaporizable and condensable within the workingtemperatures of the differential assembly. The purpose of the heat pipeis to decrease the temperature of the lubricating fluid in the axleassembly. If the temperature of the lubricant gets to high, thelubricant will break down decreasing viscosity and its ability toeffectively lubricate the gear assembly. The present inventioneffectively maintains the fluid lubricant at acceptable operatingtemperatures.

The heat pipe contains a working fluid such as water, or a sodium basedfluid or other acceptable working fluids. In liquid form, the workingfluid collects at the bottom of the heat pipe due to the force ofgravity. The bottom of the heat pipe is submersed in the pool of axlelubricant and causes the working fluid to vaporize (latent heat ofvaporization) thus reducing the temperature of the lubricating oil. Thevapor then travels up to a condensing portion where the vapor condensesgiving up heat to an external environment. The condensed liquid thenreturns to the evaporative portion where the cycle continues. Thearrangement increases the amount of heat that can be transferred fromthe axle lubricant. The structure of the preferred embodiments of thepresent invention will no be explained.

FIGS. 1-2 depict differential cover plate 1 with integral heat pipeassembly 3. A hollow loop-shaped pipe 4 forming a continuous closed loopcontaining the heat transfer fluid 5 is integrally formed with abolstered portion 7 of the cover 1. The heat pipe is simply placedwithin a molding during casting of the cover plate 1. The integralcasting facilitates good contact between the heat pipe 4 and bolsteredportion 7 to promote heat transfer there between as well as firmlyposition the heat pipe. The thick bolstered portion 7 is formed withheat dissipating fins 9 on an external surface to enhance heat transfer.As can be seen a first elongated portion 11 of the heat pipe is disposedwithin the confines of the cover 1 and consequently within the axlehousing. As can be seen in FIG. 1, the heat pipe is below the level ofthe lubricant 13, which lies just below access bore 14, and thus thefirst elongated portion of the heat pipe remains submersed in the axlelubricant during operation of the axle assembly. A second elongatedportion 12 remains substantially embedded within the bolstered portion9. The working fluid vaporizes in the first elongated portion 11 as itextracts heat from the hot lubricant. The vapor migrates to the secondelongated portion where it condenses and gives off heat through thebolstered portion 7 to the external environment. As can be readily seenthe integral heat pipe and cover assembly provide a simple solution toincreasing heat dissipation-through the axle assembly without requiringmodification to the axle assembly or remaining housing. Such anarrangement allows for easy retrofit applications to existingdifferential assemblies. The arrangement also allows for the heat pipeto be easily assembled with the cover away from the vehicle to which theaxle is installed.

FIGS. 3-4 represent an alternate embodiment of the present invention. Asin the previous embodiment, heat pipe assembly 23 is integrally securedto the cover plate 21. As in the previous embodiment the heat pipe ispreferably cast with the cover plate forming an integral connectionbetween the heat pipe and cover plate. According to this embodiment(FIGS. 3-4), the heat pipe extends through a modified bolstered portion27 of the cover plate 21, such that the second elongated portion 31 isdisposed external to the cover plate and axle housing. A plurality ofheat dissipating fins 28 is secured to the second elongated portion ofthe heat pipe to promote heat transfer to the external environment. Theremaining portions of the embodiment of FIGS. 3-4 remains nearlyidentical to that of the previously described embodiments of FIGS. 1-2.

The heat pipe assembly 3, 23 may be filled with a sodium-based workingfluid. However, the specific fluid and concentrations of solubleelements may be chosen to maintain a temperature to which the heat is tobe transferred which is largely dependent on the desired operatingtemperature of the lubricating oil such as not to exceed 200 degrees.While this present embodiment does not include a capillary structure orwick, one may be incorporated to the extent it enhances the evaporativecycle. The working fluid must also be chosen to be compatible with thematerial of the heat pipe to avoid undesirable reactions. For example,the heat pipe 3, 23 and cover 1, may be made of aluminum, copper orstainless steel or other suitable materials.

FIGS. 5-6 depict sectional views of additional embodiments of thepresent invention. Referring to FIG. 5, a rear cover 101 is secured to adifferential housing containing differential gearing to allowdifferential rotation between a pair (one shown) of output shafts 205. Apinion gear 206 drives a ring gear 207 which in turn rotates adifferential case containing differential gears (schematicallyrepresented by reference numeral 208) as is commonly known in the art.The cover 101 is simply bolted to a rear potion of the housing as isconventional in the art. The cover plate 201 preferably contains anintegrally formed reservoir 202 in fluid communication with pool oflubricant 213 in the housing 201. The heat pipe assembly 203 contains afirst evaporative end 211 disposed within the pool of lubricant 213 andincludes a plurality of heat dissipating fins 211 a also submersed inthe lubricant. The heat pipe extends through the cover plate 1,reservoir 202, to the external environment to condensing portion 212which also includes a plurality of heat dissipating fins 212 a. The heatpipe assembly 203 also preferably includes a wick member 216 disposedwithin said heat pipe to promote transfer of working fluid from saidevaporative heat receiving zone 211 to the condensing heat emitting zone212 through capillary action. The wick member may be made for example ofa metal mesh.

FIG. 6 represents a slightly modified version of the embodiment depictedin FIG. 5. In this embodiment, the evaporative portion of the heat pipe213 extends substantially vertical within the reservoir 202 as tosubstantially horizontal as the heat pipe 211 of the embodiment shown inFIG. 5.

In the embodiments of FIGS. 6-9 two heat pipes 203 a, 203 b, areemployed each containing separate evaporative cycles as in the previousembodiments. However, a first set of heat dissipating fins 412 ainterconnects each of the heat pipes in the heat dissipating/condensingzone of the assembly. A second set of heat dissipating fins 411 ainterconnects each of the heat pipes 203 a, 203 b in the heatreceiving/evaporating zone of the assembly as shown in FIGS. 8-9.

As previously indicated the specific materials may be selected based onthe material specified for the cover plate and operating temperature ofthe lubricating fluid of the axle assembly. The heat pipe, or envelopemay be composed of a durable material able to withstand environmentalcorrosion while being lightweight. Aluminum, copper and even some typesof plastics may be employed. In the embodiments shown in FIG. 1-4 therear cover is preferably made of die cast aluminum and the heat pipeenvelop made of aluminum with a sodium based working fluid containtherein. In the remaining embodiments metals such as aluminum, stainlesssteel or copper may be employed. Such metals provide sufficient strengthto be able to contain high vapor pressures as higher workingtemperatures. The envelope may also be somewhat flexible, or bendablesuch as tygon tubing. The function of the wick is to transport theworking fluid from the condenser to the evaporator via capillary action.The shape may be varied in form and can be made of various materialssuch as a metal screen. However, powdered metals, metal foams, sinteredmetals, felt type metals as well as some types of plastics or even glassmy be employed so long as it is compatible with the working fluid andheat pipe envelope material. A wick may also be omitted forming athermosyphon as in the embodiments of FIGS. 1-4. It is finally notedthat certain combinations of working fluid and envelopes which mayproduce non-condensable gasses should be avoided. These gases may resultfrom a chemical reaction between the envelope and working fluid. Forexample, an aluminum envelope and water will produce AIO and hydrogengas. Excessive accumulation of non-condensable gasses will cause theheat pipe to fail. However, it is well within the knowledge of one ofordinarily skill in the art to avoid such unacceptable combinations assuch are well documented in the art.

While the foregoing invention has been shown and described withreference to a preferred embodiment, it will be understood by thosepossessing skill in the art that various changes and modifications maybe made without departing from the spirit and scope of the invention.For example additional exemplary embodiments are shown in FIGS. 1-13which are also beleive to be within the spirit and scope of the presentinvention. For example, referring to FIG. 10, the heat pipe may extendwithin the housing beyond the cover plate. The heat pipe may also extendsubstantially horizontally as it emerges from the cover plate as shownin FIG. 11.

1. An axle assembly for a motor vehicle, said axle assembly comprising:an axle housing provided with a supply of liquid lubricant; a coverremovably secured to said housing; and at least one a sealed heattransfer pipe mounted to said cover and, said heat transfer pipeincluding an heat-receiving zone, a heat-emitting zone and a heattransfer fluid that flows there between, wherein said fluid beingevaporated in said heat-receiving zone and condensed in saidheat-emitting zone to promote heat transfer between said lubricant andan external environment; wherein said heat-receiving zone is at leastpartially immersed in said lubricant when said cover is secured to saidhousing.
 2. The axle assembly according to claim 1, wherein said heatpipe is formed as a hollow loop-shaped pipe forming a continuous closedloop containing said heat transfer fluid.
 3. The assembly according toclaim 2, wherein said loop shaped pipe include at least two elongatedportions, a first elongated portion being disposed within said housingan substantially submerged in said lubricant, said loop shaped heat pipebeing cast within a bolstered rear portion of said cover.
 4. Theassembly according to claim 3, wherein a second elongated portion ofsaid heat pipe is substantially embedded within a said bolstered portionof said cover, said bolstered portion having integrally formed finsdirectly exposed to said external environment.
 5. The assembly accordingto claim 3, wherein said heat pipe extends through said bolsteredportion and includes a second elongated disposed external said housingand directly exposed to said external environment.
 6. The assemblyaccording to claim 5, said heat pipe further includes a plurality ofheat transfer fins affixed to said second elongated portion of said heatpipe.
 7. The assembly according to claim 2 wherein said heat transferfluid is sodium based solution.
 8. An axle assembly for a motor vehicle,said axle assembly comprising: an axle housing containing gears tofacilitate differential rotation between a pair of driven output gears,said housing containing a pool of liquid lubricant; a cover removablysecured to said housing to provide access to said gears within saidhousing; and at least one a substantially sealed heat transfer pipefixed to said cover and removable therewith relative to said housing,said heat transfer pipe including a heat-receiving zone, a heat-emittingzone and a working fluid, wherein said working fluid is evaporated insaid heat-receiving zone and condensed in said heat-emitting zone topromote heat transfer between said lubricant and an externalenvironment; wherein said heat-receiving zone is at least partiallyimmersed in said lubricant when said cover is secured to said housing.9. The assembly according to claim 8, wherein at least one a sealed heattransfer pipe includes a pair of heat pipes each containing separateheat-receiving zones and heat-emitting zones, said pair of heat pipesbeing interconnected by a set of common heat dissipating fins.
 10. Theassembly according to claim 9 wherein said set of common heatdissipating fins includes a first set disposed proximate saidheat-receiving zone and being substantially immersed in said lubricant.11. The assembly according to claim 19, said heat pipe extends externalsaid housing to said external environment and said heat pipe furtherincluding a second set of common heat dissipating fins disposedproximate said heat-emitting zone in said external environment.
 12. Theassembly according to claim 8, wherein said cover contains an integrallyformed reservoir in fluid communication with said pool of lubricant insaid housing, said heat receiving zone of said heat pipe beingsubstantially disposed within said reservoir.
 13. The assembly accordingto claim 8, wherein said working fluid is a water based fluid.
 14. Theassembly according to claim 8, wherein said heat pipe further includes awick member disposed within said heat pipe to promote transfer ofworking fluid from said heat receiving zone to said heat emitting zonethrough capillary action.
 15. The assembly according to claim 14,wherein said wick member is formed of a metal screen.